Set the default of WEBGL_MAX_TEXTURE_SIZE to undefined

By doing so the examples will also work if WebGL is not supported.

examples/symbol-atlas-webgl.js

@@ -15,7 +15,8 @@ var atlasManager = new ol.style.AtlasManager({
   // we increase the default size so that all symbols fit into
   // a single atlas image
   size: 512,
-  maxSize: ol.has.WEBGL_MAX_TEXTURE_SIZE});
+  maxSize: ol.has.WEBGL_MAX_TEXTURE_SIZE
+});
 
 var symbolInfo = [{
   opacity: 1.0,

src/ol/has.js

@@ -124,9 +124,9 @@ ol.has.WEBGL;
 
 /**
  * The maximum supported WebGL texture size in pixels. If WebGL is not
- * supported, the value is set to `-1`.
+ * supported, the value is set to `undefined`.
  * @const
- * @type {number}
+ * @type {number|undefined}
  * @api
  */
 ol.has.WEBGL_MAX_TEXTURE_SIZE;
@@ -143,8 +143,9 @@ ol.has.WEBGL_EXTENSIONS;
 (function() {
   if (ol.ENABLE_WEBGL) {
     var hasWebGL = false;
-    var textureSize = -1;
+    var textureSize;
     var /** @type {Array.<string>} */ extensions = [];
+
     if ('WebGLRenderingContext' in goog.global) {
       try {
         var canvas = /** @type {HTMLCanvasElement} */